Wearers of contact lenses, must regularly rinse their lenses with a saline solution prior to inserting the lenses for continued use. For example, contact lenses must be rinsed after subjecting the lenses to a variety of chemical disinfection regimens necessary to rid the lenses of pathogenic micro-organisms. The saline solution typically has the same isotonicity as human tears to minimize occular irritation in the user. Rinsing the lenses with a normal saline solution will wash away potentially harmful and irritating chemicals remaining on the lenses as a result of a disinfection regimen.
Contact lens users generally react unfavourably, by experiencing untoward reactions, to the presence of a variety of preservatives commonly used in contact lens solutions, including normal saline solutions. It is desirable therefore to be able to produce contact lens products, including normal saline solutions, which are sterile, yet free of preservatives. Such solutions must be sterile in order not to introduce harmful micro-organisms into the eyes of the contact lens user.
It is known in the prior art (see Giefer, U.S. Pat. No. 4,585,488 issued 29 Apr. 1986) to place a saline solution preserved with hydrogen peroxide into a container together with a disk coated with platinum. The platinum reacts (as a catalyst) with the hydrogen peroxide to cause this preservative to become inert by splitting it into water (H.sub.2 O) and oxygen (O.sub.2) gas. The complete reaction is as follows: EQU 2H.sub.2 O.sub.2 +Platinum Catalyst.fwdarw.2H.sub.2 O.sub.2 +O.sub.2
The prior art method utilizing the above reaction involves the contact lens user adding the solution preserved with hydrogen peroxide to a non-sterile container, placing the platinum coated disk into the container, adding the contact lenses to the container and leaving the lenses to soak over night, so that by the next morning, the hydrogen peroxide will have been converted into inert water and the lenses will be soaking in pure saline solution. The contact lens user would then merely insert the lenses without risk of irritation from chemical preservatives. This prior art method is however, cumbersome, awkward and time consuming.
It is also known in the prior art to modify the aforesaid method by utilizing sodium pyruvate to decompose the hydrogen peroxide (see Houlsby, U.S. Pat. No. 4,521,375 issued 4 June, 1985). The sodium pyruvate reacts with the hydrogen peroxide to produce inert by-products including water and carbon dioxide.
It is further known in the prior art to fill an aerosol can with normal saline solution and a propellant, and then to subject the sealed aerosol can to terminal sterilization by irradiating it with gamma rays. This results in a sterile aerosol product containing normal saline solution, and free of any chemical preservatives. Such prior art aerosol products require the addition of a propellant, such as nitrogen, in order to achieve the pressure levels necessary for proper aerosol functioning. The disadvantages of such prior art irradiated aerosol products are several. Firstly, it is very expensive to conduct terminal sterilization by irradiation using gamma rays. Secondly, there are safety and hence political concerns relating to the use of radiation to sterilize products for use in the human body. Lastly, there are several practical problems related to the use of radiation, including the need to irradiate the aerosol product very shortly after the aerosol container has been filled and the fact that use of radiation on some chemicals will cause the chemicals to breakdown. This limits which chemicals may be used in such products to be sterilized by radiation.
An additional problem present in the prior art aerosol products relates to the difficulty in obtaining U.S. Federal Drug Administration approval for aseptic packaging of unpreserved solutions for ophthalmic use.
It is desirable to have sterile, preservative-free ophthalmic product in aerosol dispensing containers in order to maintain product sterility during use. Because the aerosol container is under pressure, there is minimal risk of micro-organisms being able to enter the sterile environment inside the aerosol can during its use. Ophthalmic solutions housed in plastic squeeze bottles may easily become contaminated during use, due to reflux action of the liquid during dispensing of the solution by the contact lens user. As a result of the aforesaid disadvantages, there is a need for an economical, safe and effective ophthalmic saline solution in aerosol packaging, which is free of chemical preservatives at the time of use of the solution by the contact lens wearer, without having been subjected to radiation exposure.